Direct drive electric vehicles have successfully used rheostat controllers for such applications as golf carts and personnel carriers. Rheostat control is quite efficient for transferring battery energy to shaft power at the wheels providing the vehicle is diven at maximum speed over reasonably level terrain.
Electric cars operating in stop and go city traffic and up steep hills require more complex control systems. One approach has been to develop controls which switch between the several battery terminals to provide a number of voltages for powering the electric motor. In between each of the selected voltages, rheostat, silicon controlled rectifier or other solid state device control circuit is used. This type of controller tends to be complicated in that it requires the use of high current relays, current and voltage sensors, current limiters and speed sensors.
Another solution that has been used is to include a 3 speed transmission of the conventional automotive type between the electric motor and the vehicle drive wheels. If used correctly this approach can appreciably reduce the maximum current drawn from the battery since mechanical multiplication is used to increase wheel torque rather than high current drains on the battery. However, since an electric motor draws high currents when loaded to torque values near the stall level, it has not been very practical to use a manually shifted transmission. Recent trends have been toward use of an automatic transmission with a torque converter similar to those used in current gasoline powered automobiles. The inherent inefficiency of the torque converter brings about a drop in overall efficiency for transferring battery energy to shaft power at the wheels.
This invention incorporates features from my earlier invented torque responsive transmissions (U.S. Pat. Nos. 3,803,932, 3,874,253 and 4,098,147) to vary the drive ratio between a battery powered electric motor and the output to the vehicle wheels.
The operator of a vehicle equipped with this invention, on depressing the accelerator pedal, will activate an off-on switch to energize the battery powered motor. As the electric motor comes up to rated speed, it initially has no load on it since the torque responsive Waddington drive transmission will be in a zero output speed configuration. However, as the accelerator pedal is depressed beyond the point where the motor is actuated, the Waddington drive responds by applying torque to the transmission output shaft. The resulting input-to-output shaft turning ratio will be directly related to the torque required to accelerate the vehicle versus the torque being supplied by the motor. Using the Waddington torque responsive transmission, the electric motor can run at constant speed under all operating conditions. The result is that use of my invention produces an electric vehicle which is more efficient than is available using current art.